The present invention relates generally to actuator latch systems for use in disc drives. More particularly, the present invention relates to an improved inertial latch for dual actuator latch systems.
When a disc drive is not in operation, the actuator, which carries the read/write head, is parked, either within a landing zone with its read/write head resting directly on the disc surface or at a parking ramp located off the disc surface. Several types of latches are used for restraining or preventing undesirable movement by a parked actuator.
Air latches are sometimes used, one example of which is described by Hickox et al. in the U.S. Pat. No. 5,555,146 entitled xe2x80x9cAnti-Rotation Air Vane Inertia Latchxe2x80x9d issued Sep. 10, 1996. An air latch is typically designed to be in a closed position in engagement with the actuator until the disc drive comes into operation and generates the air flow about the spinning discs which opens the air latch to release the actuator. To maintain the start up torque of the disc drive at a reasonably low level, the air latch is typically designed for a maximum latch force of about 30000 radianxc2x7sxe2x88x922. Furthermore, to maximize the unlatching force, an air latch is typically designed such that it tends to open when the disc drive experiences an externally induced rotational shock in the potentially most damaging direction. This direction is that which causes the actuator to swing off the parking ramp onto the disc or to swing from the landing zone into the data zone of the disc, resulting in the read/write head coming into abrasive contact with the disc surface and creating possibly irreparable damage to the data stored on the disc. This direction may be clockwise or counter-clockwise depending on the design and relative position of the disc drive components. When the disc drive is spinning down, there is a period of time when the air latch will not be able to perform as intended and thus not be able to guard against even low levels of rotational shock.
A magnetic latch uses magnetic forces to lock the actuator at the desired position, that is, at its parked position. The stronger a magnetic latch is, the more effort is required to overcome the latch force during disc drive start up when the actuator has to be set in motion. This inherent constraint results in the design of magnetic latches which generally do not retain the actuator when the disc drive experiences an external rotational shock of more than 15000 radianxc2x7sxe2x88x922.
A conventional inertial latch is typically mounted for rotation about a pivot, and includes a weighted portion and hook portion. In response to a sufficiently strong rotational shock applied to the disc drive, the hook portion rotates about the pivot to engage a receiving hook protruding from the actuator. A biasing mechanism is generally employed to bias the inertial latch in an opened state in which it is not engaged with the actuator. Only when the rotational shock is sufficiently high will the inertial latch overcome the biasing force and move to engage the actuator.
In the U.S. Pat. No. 5,877,922 entitled xe2x80x9cDual Latch Apparatus for Restraining a Direct Access Storage Device Actuatorxe2x80x9d, issued Mar. 2, 1999, Boutaghou proposed a dual latch apparatus which prevents actuator movement at both low and high levels of rotational shock. A magnetic latch assembly or an electromagnetic latch assembly is used to prevent actuator movement in the presence of relatively low levels of rotational shock. A separate inertial latch assembly is employed to restrain the actuator under relatively high levels of rotational shock. However, there exists a transitional range of acceleration levels at which the magnetic latch assembly may allow the actuator to be released before the inertial latch assembly is actuated to restrain the actuator.
The reliability of the actuator latching system can be critical to maintaining the data integrity of a disc drive. Therefore there remains a need for an improved latching system which is more reliable over a continuous range of shock levels, particularly as disc drives are nowadays incorporated into portable devices which significantly increases the risk of a disc drive experiencing an externally induced high rotational shock. The present invention provides an improved solution to meet this need, and offers other advantages over the prior art.
The present invention relates to an improved disc drive actuator latch system for restraining the read/write head from moving across the disc surface when the disc drive is not in operation. In a disc drive, an actuator is pivotably mounted to the base of a disc drive by an actuator pivot. A yoke extends from the actuator pivot to support a voice coil over a voice coil magnet. The disc drive includes a magnetic latching system which is formed by a third latch member that is joined to the yoke and a fourth latch member that is mounted to the base. There is provided an inertial latching system which includes a first latch member configured to engage a second latch member at a junction point. The first latch member includes a latch pivot mounted to the base. One side of the latch pivot extends to form a first arm whilst a balancing mass is found at another side of the latch pivot. Joined to the first arm is a finger which provides a contact line ending in a proximal point. The second latch member has a contact surface which provides a contact point configured for contact with the contact line.
In a most preferred embodiment of the present invention, the inertial latching system is configured such that the ratio of a first length to a second length is smaller than the ratio of a third length to a fourth length. The first length is defined as the distance from the proximal point to the junction point, the second length is defined as the distance from the proximal to the latch pivot, the third length is defined as the distance from the contact point to the junction point, and the fourth length is defined as a distance from the contact point to the actuator pivot.
The inertial latching system is configured such that the contact line is longer than the second length, and preferably, the contact line is at least five times as long as the second length. The finger is formed such that the contact line is at an obtuse angle with a line joining the proximal point to the latch pivot. The finger is further formed such that a line extending from the actuator pivot to the contact point forms a positive angle with the contact line.
The first latch member preferably includes a secondary magnetic latch configured to bias the first arm away from the yoke. The secondary magnetic latch may be a second arm which extends transversely from the first arm along one side of the voice coil magnet. A ferromagnetic piece of material is supported by the second arm, such that when the second arm is in abutment with the voice coil magnet, the first latch member is not in engagement with the second latch member. In a most preferred embodiment, the second latch member extends from the yoke in a direction generally perpendicular to the yoke. The disc drive is configured such that the maximum displacement of the contact point is less than the range of the magnetic latching system. The first latch member may further include a pin extending from the first arm in a direction generally perpendicular to the yoke to prevent the first arm from moving under the yoke. The disc drive may also include a post fixed to the base such that when the first arm is in abutment with the post, the second length is at its maximum.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.